Collaborative Research: A Pilot Study of Simultaneous Parameter and State Estimation in Coupled Ocean-Atmosphere General Circulation Models Using the Ensemble Kalman Filter

海洋大气环流模式(OAGCM)表现出明显的模式偏差，如热带辐合带冷舌复合体的热带偏差。这种偏差的很大一部分是由于模型参数的不确定性。然而，到目前为止，OAGCM中的参数调整仍然处于初级阶段。这一合作项目将开发一种新的战略，利用基于集合的数据同化战略，在OAGCMS中优化系统参数，重点关注突出的热带偏向问题。在现有耦合数据同化系统的基础上，将开发一个用于同时估计模式参数和状态的自适应耦合集合卡尔曼滤波系统(AcEnKF)。将研究不同的同化技术，以寻求OAGCMS参数优化的有效方法，以及与热带气候系统中气候学和气候变率的参数优化相关的耦合动力学。这项工作有望首次对基于集成的OAGCMS参数优化策略进行全面评估。这项研究还将阐明热带气候系统耦合动力学的机制及其对模式参数的敏感性。尽管存在潜在的困难，但这项试验性研究是在改进OAGCMS方面向前迈出的重要一步。这项活动具有重大的更广泛的影响：它将为全球海洋观测和监测系统的系统改进奠定基础，更广泛地说，为未来的耦合地球系统模型奠定基础。

Ocean Atmosphere General Circulation Models (OAGCM) exhibit significant model biases, e.g., the tropical bias in the Intertropical Convergence Zone cold tongue complex. A significant part of such biases is due to uncertainties in the model parameters. Thus far, however, parameter tuning in OAGCMs remains rudimentary. This collaborative project will develop a novel strategy for systematic parameter optimization in OAGCMs, using an ensemble based data assimilation strategy, focusing on the outstanding tropical bias problem. Building on an existing coupled data assimilation system, an adaptive coupled ensemble Kalman Filter system (AcEnKF) for a simultaneous estimation of model parameter and state, will be developed. Different assimilation techniques to search for an effective method of parameter optimization in OAGCMs will be studied, as also coupled dynamics relevant to parameter optimization in the tropical climate system for both the climatology and climate variability. The work is expected to give the first comprehensive evaluation of the ensemble based strategy for parameter optimization in OAGCMs. The study will also shed light on the mechanism of the coupled dynamics of the tropical climate system and its sensitivity to model parameters. In spite of potential difficulties, this pilot study represents a significant step forward in the improvement of OAGCMs. This activity has significant broader impacts: it will lay a foundation for a systematic improvement of OAGCMs and, more generally, future coupled earth system models.